The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.
In order to cope with the frequency resource depletion and to increase the utility of frequencies, recent mobile communication systems employ a TDD (Time Division Duplex) scheme which utilizes a downlink (DL) band and an uplink (UL) band at the same time. Mobile communication systems employing a TDD include TDD-SCDMA (Time-Division Synchronous CDMA), WIMAX (World Interoperability for Microwave Access), Wibro (Wireless Broadband Internet), TD-LTE (Time Division Long Term Evolution), etc.
The TDD scheme differs from an FDD (Frequency Division Duplex) in that a downlink signal and an uplink signal are temporally separated from each other. Sharing a single frequency band by the downlink and the uplink in the TDD scheme is from a collision between the downlink signal and the uplink signal because both the signals occupies different time slots. Therefore, a TDD scheme distinguishes between the downlink signal and the uplink signal by using a TDD switch, unlike the FDD that utilizes a duplexer.
However, a TDD system which is not provided with TDD switching signals from a base station, requires a separate apparatus for detecting TDD sync signals and for generating TDD switching signals so as to perform a temporal control of a TDD switch.
Typically, a distributed antenna system is composed of a head unit and a remote unit. These units are connected to each other through an optical link. A TDD switch should reside at each of the head unit and the remote unit in order to provide TDD communication services.
The head unit and the remote unit respectively detect a TDD sync signal and generate a control signal to control a downlink signal and an uplink signal.
For detecting TDD sync signals, a radio frequency (RF) power detection method has been used. The RF power detection method is to detect the sync signals by determining the presence or absence of RF power of a downlink signal. As for LTE signals, sync signals are contained in an SS (Special Switching) subframe within a frame. However, such a TDD sync signal detection method has suffered from low reliability since it performs switching operations simply based on the presence of an RF power.